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Community and Q&A

Sealed Crawl Space Ventilation

vicktown | Posted in General Questions on

I am in the process of conditioning my crawl space in southern Ontario. The ground is very sandy and the foundation in 100+ year old stone. I am planning on using 2 layers of 6 mil poly (10 mil if I can find it) to cover the ground and using a spray foam on the foundation walls and up into the joist spaces. The crawlspace is about 2-3 feet high and covers about 700 square feet.

I have been receiving mixed messages on how to create an air flow in the space and could use some tips. I was planning on adding 1 or 2 heating vents and possibly a cold air return or passive vent into the home. I can see this working in the winter when the furnace is on, but not generating enough air movement in the winter when the furnace is off.


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  1. Expert Member
    Dana Dorsett | | #1

    There is no need to fully condition the space, just provide sufficient air exchanges that you don't get toxic buildups of unsavory gases or mold. If the air exchange with the fully conditioned space air is only one full volume per day it's more than enough, and even once per week might be adequate. Small fans on interval timers can probably get you there.

  2. Expert Member
    ARMANDO COBO | | #2

    It appears you have a good grasp on how to condition your crawl space, Down here in the US, our code (2009 IRC, Sec 408.3) requires to install a 6 mil vapor retarder; however, I do believe one should only install a 20 mil which we can find at any hardware store, to avoid tears and moisture leaking in.
    As far as ventilation we have 2 choices: 1. Continuously exhaust fan at 1cfm/50sf of floor area and an air pathway from the commons area; or 2. Conditioned air supply at 1cfm/50sf of floor area and a return air pathway to the common area.

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